In recent years, hybrid cars and electric cars have been attracting attention from an environmental protection viewpoint, and their development has progressed rapidly. These cars have a configuration whereby a driving force of driving the wheels is obtained by converting direct current electric power from a power supply having a secondary battery to alternating current electric power, and driving a motor by means of alternating current electric power. Normally, a hybrid car is an electric car that uses both an engine and a motor, and is a kind of electric car in a broad sense. Therefore, for convenience, in this specification the term “electric car” is used in a broad sense that includes a hybrid car unless specifically indicated otherwise.
With an electric car of this kind, there is a particular demand for the accuracy of battery deterioration detection to be improved in order to correctly ascertain travel distance, battery life, and so forth.
Conventionally, the apparatus described in Patent Literature 1, for example, has been known as a vehicle battery deterioration determination apparatus. In Patent Literature 1, a technology is disclosed whereby when an electrical load connected to a battery is used, a voltage change of a battery voltage detected thereafter is calculated, and battery deterioration determination is performed by comparing the detected voltage change with a predetermined determination value. An electrical load is, for example, an air conditioner, power steering, headlights, brake lights, a radiator fan, or the like. Voltage change is calculated as a change in voltage over a predetermined time (that is, a voltage change trend) or a drop in battery voltage for the electrical load. By means of this configuration, the technology in Patent Literature 1 enables change over time of a battery to be detected accurately as battery deterioration, and the occurrence of starting trouble, stalling, or the like due to a low battery charge to be promptly reported to the driver.